Figure 3.6 shows filtrate pressure and TMP vs process time for two pilot-scale hollow-fiber microfiltration runs run at different flow rates. Which conclusion is most consistent with the figure and Gottschalk’s discussion?

Question

BlackTom AI · Accepted Answer

TMP rises when membrane resistance increases due to fouling, while filtrate pressure (permeate-side pressure or permeate flow indicator) falls as permeate flux declines — so a simultaneous TMP increase and filtrate pressure drop signals rapid fouling.

1) Relevant knowledge points and concepts
- Transmembrane pressure (TMP) is the driving pressure across the membrane; for constant crossflow conditions, increased membrane resistance (fouling or cake formation) requires higher TMP to maintain flux, or alternatively flux falls if TMP is held constant.
- Filtrate (permeate) pressure or permeate flow behavior reflects actual permeate production; a sudden drop in filtrate pressure (or permeate flow) indicates loss of permeation.
- Rapid membrane fouling/cake formation increases resistance quickly, producing the characteristic TMP rise and permeate/filtrate drop described by Gottschalk.

2) Step-by-step reasoning
- Observe the plotted curves: at a particular process time the filtrate pressure curve shows a sharp downward excursion while the TMP curve simultaneously climbs steeply.
- Interpreting these trends: a sharp TMP rise means the system needs higher driving force to push liquid through the membrane; the filtrate pressure/flow drop means less permeate is being produced.
- The synchronous nature of the two changes implies an abrupt increase in membrane resistance (rapid fouling or pore blockage), not a benign operating change.

3) Intermediate steps/observations
- Before the event: relatively stable filtrate pressure and low TMP (normal operation).
- During the event: filtrate pressure plunges (less permeate), TMP surges (more pressure needed).
- After the event: TMP may remain elevated until cleaning or conditions change.

4) Why the correct answer is correct
- The simultaneous filtrate-pressure drop and TMP rise are the textbook signature of rapid fouling: the membrane becomes less permeable, so TMP must increase to try to maintain flux, but permeate output falls.

5) Why other options are incorrect
- “Halving flow rate causes TMP to spike…desirable”: changing flow rate alone does not necessarily cause that signature and an undesired TMP spike is not generally “desirable.”
- “Higher flow rate always improves yield…”: higher crossflow can reduce fouling but does not always improve yield and may increase shear or energy cost; “always” is false.
- “Filtrate pressure and TMP are unrelated”: they are directly related through flux and membrane resistance, so this is false.

6) Conclusion
The observed patterns and Gottschalk’s discussion support the statement: “A sharp drop in filtrate pressure together with a rise in TMP indicates rapid membrane fouling.” This matches the provided correct answer.

Figure 3.6 shows filtrate pressure and TMP vs process time for two pilot-scale hollow-fiber microfiltration runs run at different flow rates. Which conclusion is most consistent with the figure and Gottschalk’s discussion?单项选择题

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